The long-term objective is a clearer understanding of the functional organization of the mammalian visual cortex and of its development. The specific aims are: 1) To determine the contribution of inputs from on-center and off-center retinal ganglion cells to the response properties of neurons in striate and extrastriate visual cortex, and the extent to which these inputs form anatomically separate channels; 2) To examine the development of the on/off system at the levels of the lateral geniculate nucleus and striate cortex, and to test whether developmental plasticity, analogous to that previously found in the ocular dominance system can be demonstrated; 3) To determine whether the layer-specific morphologies and connections of visual cortical neurons are determined at the time of cell generation, or whether the young neurons can respond to a variety of environmental cues as they migrate into the cortical plate. Achievement of these goals will help in understanding functional and developmental abnormalities of the human visual system and factors aiding and hindering adaptive plasticity in cerebral function. Methods include single-unit recording in normal animals and after pharmacological inactivation of on-center retinal ganglion cells, neuro-anatomical tracer studies, transplantation of dissociated, labeled cells between fetal and newborn animals, and the anatomical study of cell differentiation after the elimination of early-born populations of visual cortical neurons.